PROJECT SUMMARY/ABSTRACT Preterm birth remains a significant cause of neonatal morbidity and mortality. Intra-amniotic infection and inflammation are important triggers for early preterm birth, which is associated with fetal injury mediated by cytokines and other inflammatory mediators in the amniotic fluid and fetus. The objective of this proposal is to establish the efficacy and safety of a novel selective allosteric interleukin-1 receptor (IL-1R) inhibitor (Rytvela) as an antenatal therapeutic strategy to prevent fetal injury and PTB. In pregnant mice, we have strong evidence that Rytvela is a potent suppressor of preterm birth and fetal injury induced by either lipopolysaccharide or lipotechoic acid. To enable translation of these discoveries to human pregnancy, we propose to test the efficacy and determine pharmacokinetics of Rytvela in a pregnant nonhuman primate model of preterm labor induced by Group B Streptococcus (GBS), a clinically important bacterium that colonizes the vagina and can cause preterm labor and neonatal sepsis. Our unique chronically catheterized nonhuman primate model has the greatest relevance to human pregnancy of any animal model and allows sampling in normally inaccessible compartments (amniotic fluid, maternal and fetal blood) multiple times without disrupting the pregnancy. New preliminary studies added to this resubmission demonstrate: 1) inhibition of preterm birth by Rytvela for at least 7 days (clinically significant endpoint), 2) determination of Rytvela pharmacokinetics in a rat model, 3) ability to quantify Rytvela using mass spectrometry in plasma for pharmacokinetics studies, and 3) incorporation of novel technology (Digital Spatial Profiling) to study immune responses at the maternal-fetal interface. In Aim 1, we will determine Rytvela pharmacokinetics in our NHP model and establish if IL-1 inhibition by Rytvela delays the onset of GBS-induced preterm labor. Aim 2 will determine if IL-1 inhibition by Rytvela can ameliorate inflammatory injury to the placenta, fetal lung and brain using three high-throughput multiplexed analyses: 1) multidimensional flow cytometry to quantitate cell populations, 2) Digital Spatial Profiling to interrogate immunologic protein expression and pathway activation in discrete tissues (amnion, chorion, decidua) of the placental chorioamniotic membranes, and 3) single cell RNA-Seq for transcriptomic profiling of regulatory gene networks within single cells in placental tissues. These experiments represent a natural progression of preliminary studies in multiple animal models and are essential to determining whether IL-1 is a viable molecular target for the prevention of preterm birth and fetal protection.